GB1578031A

GB1578031A - Method and apparatus for testing liquids

Info

Publication number: GB1578031A
Application number: GB1201976A
Authority: GB
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1977-03-18
Filing date: 1977-03-18
Publication date: 1980-10-29

Description

(54) METHOD AND APPARATUS FOR TESTING LIQUIDS (71) We, IMPERIAL CHEMICAL INDUSTRIES LIMITED, Imperial Chemical House, Millbank, London SW1P 3JF, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention comprises a method and apparatus for testing liquids.

It is desirable to be able to identify changes in liquids present between two points, for example due to a change of level or nature of liquids present in vessels used in industrial processes.

This invention provides apparatus for testing fluids by transmitting sonic vibration through them and detecting changes in the fluids in terms of a change in the velocity of sonic vibration passing through them.

This invention comprises apparatus for testing liquids in vessels which apparatus comprises means outside the walls of the vessel to transmit pulses of sonic vibration through a region to which a liquid to be tested has access and means outside the wall of the vessel to detect sonic vibration which has passed through the said region and means to cause transmission of the said sonic vibration during a first time interval or intervals and to discriminate between the presence or absence of liquid or a change in the nature of the liquid present in the said region by determining whether an output signal from the means to detect the sonic vibration occurs within a second time interval or intervals which is not coincident with the first time interval or intervals.

The apparatus is suitably used to detect changes of level of a liquid or changes of interfacial level between two immiscible liquids.

The time intervals may be related so that the said output signal is normally detected.

If it is necessary to maintain the liquid at a minimum level the second time interval or time intervals may be of similar length to that of the first time interval or time intervals but at a delay after it or them corresponding to the time taken for sound to pass from the transmitter to the detector through the liquid. By this means an output signal as aforesaid is only available in the second interval or intervals when the liquid is in position and the apparatus will be fail-safe in that should the apparatus fail, it will produce an indication corresponding to the liquid having fallen below the minimum level.If it is desired to provide fail-safe apparatus for an interfacial level at a maximum level between two liquids the apparatus should operate using time intervals related so that an output signal as aforesaid is only available in the second interval or intervals when the upper liquid is in position.

The duration of the second time interval or intervals may be greater than that of the first time interval or intervals or less than that interval or intervals if desired For example if an interfacial level between two immiscible liquids is to be detected and the speed of sound in the liquids is very similar it may be desired to select a second interval corresponding to the leading or following edge of the first when transposed in time by an interval corresponding to the time taken for sound to pass through one of the liquids from the transmitter to the detector.

In use the apparatus is used in conjunction with a vessel to which the liquid to be tested has access, the transmitter and detector being arranged such that sonic vibration is passed from the transmitter to the detector through liquid in the vessel.

Suitably the transmitter and detector may be on opposite sides of the vessel and are suitably secured by adhesive to the outside of its walls. If desired, however, the transmitter and detector may be situated side by side and sonic vibration may be passed between them by reflection, for example from the opposite wall of the vessel or by a reflector element disposed within the vessel.

It is preferred that the duration of the second interval(s) should be similar to that of the first, for example the ratio of either interval to the other is preferably not greater than 20 : 1, and more preferably is not greater than 10 : 1. It is preferred that the second interval(s) should be separated in time from the first by preferably at least 0.01 milliseconds.

The frequencies of the sonic vibration are preferably in the range 0.05 to 10 M. Hertz, and preferably 0.5 to 5.0 M. Hertz.

The path of transmission of the sonic vibration between the transmitter and detector is preferably in the range 50 mm to 10 m.

It is preferred that when the first interval(s) is transposed by a time lag corresponding to the time taken for sound to pass from the transmitter to the detector when the liquid to be tested is in place that the first and second intervals should be coincident or that one should lie within the other, though if desired there may be overlap between the intervals.

The invention will now be described with reference to the drawing which is a diagramatic representation of apparatus according to the invention. The master oscillator 1 feeds voltage pulses of a frequency of 1000 per second and a duration of 0.5 milliseconds through a Zener barrier 2, which is optional and serves to limit the energy passing from it in order to secure the intrinsic electrical safety of apparatus beyond it if such apparatus is operating in areas of potential hazard. The Zener barrier passes a signal along a long cable to the area of potential hazard to a pulser 4 which reconstitutes the wave-form received from the Zener barrier as narrow pulses of power of a duration of 0.2 microseconds which are fed to transducer 5. Transducer 5 is secured by adhesive to the wall of a tank in which liquid is to be maintained at a minimum level.The transducer on receipt of a pulse ring at 2.5 megahertz for 20 microseconds with decreasing energy.

Transducer 6 is situated on an opposite wall of the tank and secured to it by adhesive. It is sensitive to the vibration produced by transducer 5 and feeds signals detected to preamplifier 7 which passes an amplified signal along a long cable to a Zener barrier 8 which is in a safe area and which prevents any reverse energy flow from later parts of the apparatus to preamplifier 7. Zener barrier 8 feeds a signal to amplifier 9 which is adjustable in its frequency response and gain. The amplifier 9 feeds a voltage comparator 10 which provides a standard height pulse from any input signal above a settable threshold level thus providing square waves synchronised with sounds received by transducer 6.The square waves are fed to delay monostable 11 which changes the square wave peak width and thus produces a single square wave from a succession of pulses associated with each sonic pulse received.

The master oscillator 1 also feeds a delay monostable 12 which produces pulses of adjustable width from the incoming impulse and in turn feeds delay monostable 13 which produces a square wave of adjustable width in response to the ending of each square wave peak received from the delay monostable 12. This delay monostable 13 provides a succession of peaks of adjustable width commencing at an adjustable time interval after the receipt of a pulse from master oscillator 1 and thus after the commencing of vibration by transducer 5. Delay monostable 13 controls a gate 14 through which signals from the delay monostable 11 are fed to retriggerable monostable 15. By this means signals received by transducer 6 may be fed to retriggerable monostable 15 if they are in defined time periods set by delay monostables 12 and 13.Retriggerable monostable 15 remains in the same state if regular pulses are fed to it but in the event that such pulses are not received it changes its output state which is fed tO relay and alarm 16 which gives an alarm if the signal fails.

The apparatus operates as follows: - The time interval required for the passage of sonic vibration from transducer 5 to transducer 6 in the presence of the liquid is set as the pulse width of delay monostable 12.

Delay monostable 13 is set to give a greater pulse width than delay monostable 11. When the master oscillator 1 produces a signal, sonic vibration is transmitted by transducer 5 and the gate 14 is opened for an interval of time sufficient to enable any signal received by transducer 6 in the presence of the liquid to be transmitted to retriggerable monostable 15. In the event of liquid falling below the desired level or of the apparatus failing, no signal is transmitted from the triggerable monostable 15 to relay and alarm 16 and thus an alarm is given. The apparatus thus fails safe.

WHAT WE CLAIM IS: 1. Apparatus for testing liquids in vessels which comprises means outside the wall of the vessel to transmit pulses of sonic vibration through a region to which a liquid to be tested has access and means outside the wall of the vessel to detect sonic vibration which is passed through the said region and means to cause transmission of the sonic vibration during a first time interval or intervals and to discriminate between the presence or absence of liquid or a change in the nature of the liquid present in the said region by determining whether an output signal from the means to detect the sonic vibration occurs within a second time interval or intervals which is not coincident with the first time interval or intervals.

2. Apparatus as claimed in Claim 1 in

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. interval to the other is preferably not greater than 20 : 1, and more preferably is not greater than 10 : 1. It is preferred that the second interval(s) should be separated in time from the first by preferably at least 0.01 milliseconds. The frequencies of the sonic vibration are preferably in the range 0.05 to 10 M. Hertz, and preferably 0.5 to 5.0 M. Hertz. The path of transmission of the sonic vibration between the transmitter and detector is preferably in the range 50 mm to 10 m. It is preferred that when the first interval(s) is transposed by a time lag corresponding to the time taken for sound to pass from the transmitter to the detector when the liquid to be tested is in place that the first and second intervals should be coincident or that one should lie within the other, though if desired there may be overlap between the intervals. The invention will now be described with reference to the drawing which is a diagramatic representation of apparatus according to the invention. The master oscillator 1 feeds voltage pulses of a frequency of 1000 per second and a duration of 0.5 milliseconds through a Zener barrier 2, which is optional and serves to limit the energy passing from it in order to secure the intrinsic electrical safety of apparatus beyond it if such apparatus is operating in areas of potential hazard. The Zener barrier passes a signal along a long cable to the area of potential hazard to a pulser 4 which reconstitutes the wave-form received from the Zener barrier as narrow pulses of power of a duration of 0.2 microseconds which are fed to transducer 5. Transducer 5 is secured by adhesive to the wall of a tank in which liquid is to be maintained at a minimum level.The transducer on receipt of a pulse ring at 2.5 megahertz for 20 microseconds with decreasing energy. Transducer 6 is situated on an opposite wall of the tank and secured to it by adhesive. It is sensitive to the vibration produced by transducer 5 and feeds signals detected to preamplifier 7 which passes an amplified signal along a long cable to a Zener barrier 8 which is in a safe area and which prevents any reverse energy flow from later parts of the apparatus to preamplifier 7. Zener barrier 8 feeds a signal to amplifier 9 which is adjustable in its frequency response and gain. The amplifier 9 feeds a voltage comparator 10 which provides a standard height pulse from any input signal above a settable threshold level thus providing square waves synchronised with sounds received by transducer 6.The square waves are fed to delay monostable 11 which changes the square wave peak width and thus produces a single square wave from a succession of pulses associated with each sonic pulse received. The master oscillator 1 also feeds a delay monostable 12 which produces pulses of adjustable width from the incoming impulse and in turn feeds delay monostable 13 which produces a square wave of adjustable width in response to the ending of each square wave peak received from the delay monostable 12. This delay monostable 13 provides a succession of peaks of adjustable width commencing at an adjustable time interval after the receipt of a pulse from master oscillator 1 and thus after the commencing of vibration by transducer 5. Delay monostable 13 controls a gate 14 through which signals from the delay monostable 11 are fed to retriggerable monostable 15. By this means signals received by transducer 6 may be fed to retriggerable monostable 15 if they are in defined time periods set by delay monostables 12 and 13.Retriggerable monostable 15 remains in the same state if regular pulses are fed to it but in the event that such pulses are not received it changes its output state which is fed tO relay and alarm 16 which gives an alarm if the signal fails. The apparatus operates as follows: - The time interval required for the passage of sonic vibration from transducer 5 to transducer 6 in the presence of the liquid is set as the pulse width of delay monostable 12. Delay monostable 13 is set to give a greater pulse width than delay monostable 11. When the master oscillator 1 produces a signal, sonic vibration is transmitted by transducer 5 and the gate 14 is opened for an interval of time sufficient to enable any signal received by transducer 6 in the presence of the liquid to be transmitted to retriggerable monostable 15. In the event of liquid falling below the desired level or of the apparatus failing, no signal is transmitted from the triggerable monostable 15 to relay and alarm 16 and thus an alarm is given. The apparatus thus fails safe. WHAT WE CLAIM IS:

1. Apparatus for testing liquids in vessels which comprises means outside the wall of the vessel to transmit pulses of sonic vibration through a region to which a liquid to be tested has access and means outside the wall of the vessel to detect sonic vibration which is passed through the said region and means to cause transmission of the sonic vibration during a first time interval or intervals and to discriminate between the presence or absence of liquid or a change in the nature of the liquid present in the said region by determining whether an output signal from the means to detect the sonic vibration occurs within a second time interval or intervals which is not coincident with the first time interval or intervals.

2. Apparatus as claimed in Claim 1 in

which the time intervals are related so that the said output signal is normally detected.

3. A vessel to which a liquid to be tested has access which is equipped with apparatus as claimed in Claim 1 or 2.

4. A vessel as claimed in Claim 3 in which the transmitter and detector are on opposite sides of the vessel.

5. A vessel as claimed in Claim 3 in which the transmitter and detector are situated side by side and sonic vibration is passed between them by reflection.

6. Apparatus as claimed in any preceding claim in which the duration of the second time interval or intervals is similar to that of the first time interval or intervals and is separated from the first time interval or intervals by at least 0.01 milliseconds, the said separation corresponding to the time taken for sound to pass from the transmitter to the detector when the liquid to be tested is in place.

7. Apparatus as claimed in any preceding claim in which the frequency of sonic vibration is in the range 0.5 to 10 megahertz.

8. Apparatus as claimed in any preceding claim in which the path of transmission of the sonic vibration between the transmitter and detector is in the range 50 mm to 10 metres.

9. Apparatus for testing liquids substantially as described with reference to the drawing.

10. A method of testing liquids using apparatus as claimed in any of claims 1 to 9.